Andreas Tortschanoff

Improved MOEMS based ultra rapid Fourier transform infrared spectrometer

We present an improved FTIR spectrometer using a novel MOEMS actuator and discuss in detail the properties of the MOEMS component and the resulting FT-IR sensor device. Spectral resolution and the spectral range allow making use of the inherent multi-analyte detection capabilities giving the spectroscopy platform an advantage over singlewavelength IR sensors. With its further miniaturization potential due to its MOEMS core, this compact, energy efficient and robust spectrometer can thus act as transducer for portable and ultra-lightweight spectroscopic IR sensors, e.g. all purpose hazardous vapor sensors, sensors for spaceborne and Micro-UAV based IR analysis, and many more.

Optical position encoding and phase control of an electrostatically driven two-dimensional MOEMS scanner at two resonant modes

We have developed compact devices to control electrostatically driven resonant micromirrors with one and two axes. For stable oscillation with large amplitude, operation close to resonance must be ensured under varying environmental conditions. Our devices feature optical position sensing and driver electronics with closed loop control. In this contribution, we present in much detail the novel two-dimensional device and highlight specific aspects of this system.

Development, characterization and application of compact spectrometers based on MEMS with in-plane capacitive drives

With a trend towards the use of spectroscopic systems in various fields of science and industry, there is an increasing demand for compact spectrometers. For UV/VIS to the shortwave near-infrared spectral range, compact hand-held polychromator type devices are widely used and have replaced larger conventional instruments in many applications. Still, for longer wavelengths this type of compact spectrometers is lacking suitable and affordable detector arrays. In perennial development Carinthian Tech Research AG together with the Fraunhofer Institute for Photonic Microsystems endeavor to close this gap by developing spectrometer systems based on photonic MEMS. Here, we review on two different spectrometer developments, a scanning grating spectrometer working in the NIR and a FT-spectrometer accessing the mid-IR range up to 14 μm. Both systems are using photonic MEMS devices actuated by in-plane comb drive structures. This principle allows for high mechanical amplitudes at low driving voltages but results in gratings respectively mirrors oscillating harmonically. Both systems feature special MEMS structures as well as aspects in terms of system integration which shall tease out the best possible overall performance on the basis of this technology. However, the advantages of MEMS as enabling technology for high scanning speed, miniaturization, energy efficiency, etc. are pointed out. Whereas the scanning grating spectrometer has already evolved to a product for the point of sale analysis of traditional Chinese medicine products, the purpose of the FT-spectrometer as presented is to demonstrate what is achievable in terms of performance. Current developments topics address MEMS packaging issues towards long term stability, further miniaturization and usability.

A compact and portable IR analyzer: progress of a MOEMS FT-IR system for mid-IR sensing

We show results on the progress in the development of MOEMS based FT spectrometers dedicated to operate in the mid-IR. Recent research is performed within an EC-FP7 project with the goal to show the feasibility of miniaturized high performance infrared spectroscopic chemical analyzers. Exploiting the high analyte selectivity of the mid-IR paired with the inherent sensitivity of an FT-IR spectrometer, such devices could be used in a wide range of applications, from air monitoring over in-line real-time process control to security monitoring. For practical applicability in these fields, appropriate detection limits and spectral quality standards have to be met. The presented system aims at a performance to measure in the range between 4000-700 cm-1 at a spectral resolution better than 10 cm-1, which would clearly outmatch previous MOEMS based spectrometer approaches. A further technological advantage is the rapid-scan capability. The MOEMS devices oscillate at 500 Hz. A spectrometer based on this device can acquire 1,000 scans per second in forward-backward mode. The interplay of all these components with the challenges in system integration will be described in detail and experimental results will be shown, presenting a significant step forward in smart spectroscopic sensors, microsystems technology and vibrational spectroscopy instrumentation.

Design rules for a compact and low-cost optical position sensing of MOEMS tilt mirrors based on a Gaussian-shaped light source

A tilt mirror’s deflection angle tracking setup is examined from a theoretical point of view. The proposed setup is based on a simple optical approach and easily scalable. Thus, the principle is especially of interest for small and fast oscillating MEMS/MOEMS based tilt mirrors. An experimentally established optical scheme is used as a starting point for accurate and fast mirror angle-position detection. This approach uses an additional layer, positioned under the MOEMS mirrors backside, consisting of a light source in the center and two photodetectors positioned symmetrical around the center. The mirror’s back surface is illuminated by the light source and the intensity change due to mirror tilting is tracked via the photodiodes. The challenge of this method is to get a linear relation between the measured intensity and the current mirror tilt angle even for larger angles. State-of-the-art MOEMS mirrors achieve angles up to ±30°, which exceeds the linear angle approximations. The use of an LED, small laser diode or VCSEL as a lightsource is appropriate due to their small size and inexpensive price. Those light sources typically emit light with a Gaussian intensity distribution. This makes an analytical prediction of the expected detector signal quite complicated. In this publication an analytical simulation model is developed to evaluate the influence of the main parameters for this optical mirror tilt-sensor design. An easy and fast to calculate value directly linked to the mirror’s tilt-angle is the “relative differential intensity” (RDI = (I1 − I2) / (I1 + I2)). Evaluation of its slope and nonlinear error highlights dependencies between the identified parameters for best SNR and linearity. Also the energy amount covering the detector area is taken into account. Design optimizing rules are proposed and discussed based on theoretical considerations.

Optical Position Feedback for electrostatically driven MOEMS-Scanners

For MOEMS devices which do not have intrinsic on-chip feedback, position information can be provided with optical methods, most simply by using a reflection from the backside of a MOEMS scanner. Measurement of timing signals using fast differential photodiodes can be used for resonant scanner mirrors performing sinusoidal motion with large amplitude. While this approach provides excellent accuracy it cannot be directly extended to arbitrary trajectories or static deflection angles. Another approach is based on the measurement of the position of the reflected laser beam with a quadrant diode. In this work, we present position sensing devices based on either principle and compare both approaches showing first experimental results from the implemented devices

Industrial Raman mapping spectroscopy for mining applications

A Raman mapping system for detecting and discriminating minerals such as dolomite, marble, calcite and pyrite is demonstrated. The system is built from components that are suitable for industrial conditions. Together with a signal processing and a classier the system was shown to be capable of discriminating between several important classes of mineral. The technique is a potential alternative to sensing methods currently used for mineral sorting.

Application of a compact diode pumped solid-state laser source for quantitative laser-induced breakdown spectroscopy analysis of steel

Abstract. Laser-induced breakdown spectroscopy (LIBS) technology holds the potential for onsite real-time measurements of steel products. However, for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key requirement. In this contribution, we present tests with our compact high-power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid-state laser with a passive Q-switch with dimensions of less than 10  cm3. The laser generates 2.5-ns pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well-suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.

Hyperspectral light field imaging

A light field camera acquires the intensity and direction of rays from a scene providing a 4D representation L(x,y,u,v) called the light field. The acquired light field allows to virtually change view point and selectively re-focus regions algorithmically, an important feature for many applications in imaging and microscopy. The combination with hyperspectral imaging provides the additional advantage that small objects (beads, cells, nuclei) can be categorised using their spectroscopic signatures. Using an inverse fluorescence microscope, a LCTF tuneable filter and a light field setup as a test-bed, fluorescence-marked beads have been imaged and reconstructed into a 4D hyper-spectral image cube LHSI(x,y,z,λ). The results demonstrate the advantages of the approach for fluorescence microscopy providing extended depth of focus (DoF) and the fidelity of hyper-spectral imaging.

Compact DPSS-laser source for LIBS analysis of steel

LIBS-technology holds the potential for on-site real-time measurements of steel products. However for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key-requirement. In this contribution, we present tests with our novel compact high power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid state laser with a passive Q-switch with dimensions of less than 10 cm³. The laser generates 2.5 ns-pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.